1. Field of the Invention
The present invention relates to a learning and control apparatus for feedback control of an air-fuel ratio, an idle rotation number or the like in an electronically controlled internal combustion engine.
2. Conventional Techniques
As the conventional learning and control apparatus for an internal combustion engine, there can be mentioned an apparatus for learning and control of an air-fuel ratio, as disclosed in Japanese Patent Application Laid-Open Specification No. 90944/85, and an apparatus for learning and control of an idle rotation number, as disclosed in Japanese Patent Application Laid-Open Specification No. 93143/85.
The conventional techniques will now be described with reference to an apparatus for learning and control of a base air-fuel ratio, in which the air-fuel ratio is feedback-controlled to a theoretical air-fuel ratio is an aimed control value in an internal combustion engine provided with an electronically controlled fuel injection apparatus.
An electronically controlled fuel injection valve is opened by a driving pulse signal (injection pulse) given synchronously with the rotation of an engine and while the valve is opened, a fuel is injected under a predetermined pressure.
Accordingly, the injection quantity of the fuel depends on the period of opening of the valve, that is, the injection pulse width. Assuming that this pulse width is expressed as Ti and is a control signal corresponding to the injection quantity of the fuel, Ti is expressed by the following equations: EQU Ti=Tp.times.COEF.times..alpha.+Ts and Tp=K.times.Q/N
wherein Tp stands for the injection pulse width corresponding to the basic injection quantity of the fuel, which is called "basic fuel injection quantity" for convenience, K stands for a constant, Q stands for the flow quantity of air sucked in the engine, N stands for the rotation speed of the engine, COEF stands for various correction coefficients for correcting the quantity of the fuel, which is expressed by the following formula: EQU COEF=1+Ktw+Kas+Kai+Kmr+Ketc
in which Ktw stands for a coefficient for increasing the quantity of the fuel as the water temperature is lower, Kas stands for a correction coefficient for increasing the quantity of the fuel at and after the start of the engine, Kai stands for a correction coefficient for increasing the quantity of the engine after a throttle valve arranged in an intake passage of the engine is opened, Kmr stands for a coefficient for correcting the air fuel mixture, and Ketc stands for other correction coefficient for increasing the quantity of the fuel, .alpha. stands for an air-fuel ratio feedback correction coefficient for the feedback control (.lambda. control), described hereinafter, of the air-fuel ratio of the air-fuel mixture, and Ts stands for the quantity of the voltage correction for correcting the change of the flow quantity of the fuel injected by the fuel injection valve, which is caused by the change of the voltage of a battery.
In short, the desired injection quantity of the fuel is obtained by multiplying the basic fuel injection quantity Tp by various correction coefficients COEF, and when a difference is brought about between the aimed control value to be attained by the control and the actual controlled value, this difference is multiplied by .alpha. to effect the feedback control and the correction for the power source voltage is added to the feedback control.
This air-fuel ratio feedback correction control is disclosed in, for example, U.S. Pat. No. 4,284,050, U.S. Pat. No. 3,483,851 and U.S. Pat. No. 3,750,632.
However, in this air-fuel ratio feedback control, for example, when one constant driving region is greatly changed to a different constant driving region, if the base air-fuel ratio in this different stationary driving region is greatly deviated from .lambda.=1 (.lambda. stands for an actual air-fuel ratio), it takes too long a time to perform the feedback control (proportion and integration control . . . PI control) of the change of the base air-fuel ratio generated by this deviation to .lambda.=1. More specifically, even though the base air-fuel ratio has been obtained from the specific injection quantity Tp.times.COEF and the deviation of this air-fuel ratio from the theoretical air-fuel ratio has been corrected by the PI control based on .alpha., since the base air-fuel ratio is greatly changed, the base air-fuel ratio is controlled to a value greatly different from .lambda.=1 if Tp.times.COEF used up to this time is still used, and the feedback correction by similar PI control should be performed and it takes a long time to correct the base air-fuel ratio to .lambda.=1 by the feedback correction.
The control system in which the above-mentioned disadvantage is eliminated by learning the control quantity controlled by the system and increasing the respondency of the air-fuel ratio control in the same driving state has been proposed by us in Japanese Patent Application Laid-Open Specifications No. 203828/74 and No. 203829/74 and U.S. patent application Ser. No. 604,025, now U.S. Pat. No. 4,615,319, issued Oct. 7, 1986.
According to this control system, learning control of the air-fuel ratio feedback control is first carried out. More specifically, in the air-fuel ratio feedback control region, if the base air-fuel ratio is deviated from the aimed air-fuel ratio .lambda.t, since the feedback correction coefficient .alpha. is increased for compensating this gap during the process of transfer, the driving state at this time and .alpha. are detected, and a learning correction coefficient Kl based on this .alpha. is determined and stored. When the same driving state is brought about, the base air-fuel ratio is corrected to the aimed air-fuel ratio .lambda.t with a good respondency by the stored learning correction coefficient Kl. Storing of the learning correction coefficient Kl is performed for all of engine-driving state areas of a predetermined range formed by lattice division of a map of RAM according to the rotation speed of the engine and the engine-driving conditions such as the load.
More specifically, the map of the learning correction coefficient Kl corresponding to the rotation speed of the engine and the driving conditions of the engine such as the load is formed on RAM, and when the injection quantity Ti is calculated, the basic injection quantity Tp is corrected by Kl as shown by the following equation: EQU Ti=Tp.times.COEF.times.Kl.times..alpha.+Ts (1)
Learning of Kl is advanced according to the following procedures.
(i) The engine-driving state in the constant state and the median .alpha.c of control of .alpha. (the mean value of a plurality of values Kl at the time of reversion of increase and decrease of the output signal of an O.sub.2 sensor) are detected. PA1 (ii) The value Kl(old) heretofore learned, corresponding to the engine-driving state, is retrieved. PA1 (iii) The value of Kl(old) +.DELTA..alpha./M is determined from .alpha. c and Kl(old), and the storage is renewed with the obtained value (learned value) being as new Kl (new).
Incidentally, .DELTA..alpha. stands for the deviation from the standard valve .alpha.1 and expressed by .DELTA..alpha.=.alpha.-.alpha.1. The standard value .alpha.1 is ordinarily set at 1.0 as the value corresponding to .lambda.=1. M is a constant larger than 1.
An apparatus for learning and control of the idle rotation speed is applied to the case where an idle control valve is disposed in an auxiliary air passage bypassing a throttle valve and the opening degree of this idle control valve is adjusted to control the idle rotation speed. When the basic opening degree of the idle control valve corresponding to the aimed idle rotation speed for each temperature of cooling water for the engine is feedback-controlled while comparing the aimed idle rotation speed with the actual idle rotation speed, a map of learning correction quantities is formed according to the temperature of cooling water as a parameter of the engine driving state, the deviation of the feedback correction quantity from the base value is learned to correct the learning correction quantity, and the basic opening degree of the valve is corrected by this learning correction quantity to stabilize the control.
According to the above-described learning and control system which is served for controlling such an air fuel ratio of air-fuel mixture to be sucked into an engine, new learning correction coeffcient Kl(new) is operated in conformity with a formula mentioned herein-below and the preceding learning correction coefficient Kl(old) should be renewed by the Kl(new). The formula teaches that mean value .DELTA..alpha. of deviations .DELTA..alpha. of feed-back correction coefficient .alpha. from a standard value .alpha.1 is operated and the new learning correction coefficient Kl(new) is operated by adding the mean deviation value .DELTA..alpha. by a predetermined ratio (1/M) to a present or former learning correction coefficient Kl(old). EQU Kl(new).rarw.Kl(old)+.DELTA..alpha./M
In this operating manner of Kl(new), advancing speed of learning Kl significantly depends on the selected value of M which decides the ratio for adding the mean deviation value .DELTA..alpha. i.e. the weighted ratio for mean deviation values.
In general, M is selected in a region including larger numbers which range from 8 to 32 so that the deviation from the standard value .alpha.1 can be gradually reduced since the above-mentioned kind of learning control system is effective to correct the deviation which is brought about based on deterioration of parts of the engine subjected to be used for a long term.
Learning Kl is carried on at each region restricted by engine driving parameter when engine driving states are in the region. Therefore by means of prior art of the learning control system above described, the frequency of learning occasion at each engine driving region is quite different from each other, then there remains a problem that learning can hardly advance at some engine driving regions where learning occasions are quite few when the selected value of M is large.
Further, learned value of learning correction coefficient Kl may happen to be canceled or cleared after the learning has advanced to a certain level when, for instance,a connection with a battery mounted on a vehicle and the learning and control apparatus for the electrically controlled engine is cut-off. The cancellation or clearance of the learned value may forcibly occur by means of system disclosed in the Japanese Patent Laid-Open Specification No. 211742/84. In such a case of cancellation or clearance of the learned value, it must take a quite long time to reduce or correct the deviation of basic air-fuel ratio by re-learning of Kl when the value of M is set a larger one or significant deterioration takes place on parts of the engine. Consequently, expected advantage of the learning and control system can not be profitably accepted during the re-learning.
Also in the apparatus disclosed in Japanese Patent Application Laid-Open Specification No. 211738/84, there arises the problem mentioned above in connection with learning and control of the fuel injection pulse width. According to this known technique, an idle control valve is disposed in an auxiliary air passage bypassing a throttle valve, and the opening degree of the idle control valve is adjusted according to the duty ratio of a pulse signal. The preset aimed rotation speed is compared with the actual rotation speed and feedback correction is effected , and a learning correction quantity stored RAM corresponding to the rotation speed is retrieved from the actual rotation speed. The weighted mean of the feedback correction quantity and the learning correction quantity is calculated, and the data in RAM are renewed by using this mean value as a new learning correction coefficient, and the above-mentioned feedback correction quantity and learning correction quantity are added to the preset basic control value of the pulse signal to operate the control valve of the pulse signal for controlling the idle control valve. As in case of learning and control of the fuel injection pulse width, re-learning cannot abruptly catch up with the large deviation of basic control value of the pulse signal when the learned value canceled.